This invention is directed generally to monitoring/metering and more particularly to compensating for brief interruptions in the supply power for a power monitoring unit.
The art of power circuit monitoring continues to develop. Long standing monitoring systems, for example for residential use, have in the past consisted of nothing more sophisticated than fuses, and more commonly, circuit breakers which have a given power/time characteristic so that the circuit is broken or switched to an open circuit condition, usually at a power distribution center or breaker box, when the current through the protected line exceeds the power/time characteristic of the circuit breaker or fuse component or the like.
Power monitoring systems monitor the flow of electrical power in circuits through a plant or other facility. In the POWERLOGIC system manufactured by the instant assignee, circuit monitors and power meters are dedicated to power monitoring, while other compatible devices collect additional equipment information from protective relays, circuit breakers, transformers, temperature controllers, and panelboards. Electrical data, such as current, power, energy waveforms, and equipment status, is passed over a data network to one or more computers. The computers run power monitoring application software that retrieves, stores, organizes, and displays real-time circuit information in simple, usable formats. The information collected and stored in a power monitoring system helps operate a facility more efficiently. The quality of the data depends upon the accuracy of the instrumentation and the usability of the display formats.
The power meter can replace conventional metering devices such as ammeters, voltmeters, and watt-hour meters while providing other capabilities not offered by analog metering. The power meter's true root mean square (rms) readings reflect non-linear circuit loading more than conventional analog metering devices. The power meter calculates the neutral current, which can assist in identifying overloaded neutrals due to either unbalanced single phase loads or triple harmonics. Circuits can be closely monitored for available capacity by keeping track of the peak average demand current.
The power meter can provide a full complement of rms metering values to a metering display and/or via a standard communication port to a power monitoring and control system. The display is connected to the power meter with a communications cable and allows the user to view metering data and access meter setup and reset menus. The display can be mounted at a remote location relative to the power meter itself.
In power metering systems made by the Square D Company, the assignee of this application, a modular or building block system is used. This system incorporates a base unit with one or more additional units, such as a main metering circuit, a communications unit and an input/output unit or module, each of which may require a particular DC operating voltage. These operating voltages have generally been supplied through an off-line voltage regulator/converter in the base unit which supplies required DC voltages which may be tapped into for the various other modules. In order to maintain power to the various modules during relatively brief power outages, a single ride-through capacitance has been provided in the base unit.
Since this ride-through capacitance is required to provide operating power for the power metering system, a large, heavy ride-through capacitor bank is generally required. This is done to accommodate the maximum power load which may be required for a system having a maximum number of modules with the maximum power requirement. However, providing such a large capacitor bank with the base unit is relatively expensive and also adds to the required size of the base unit. Examples of such systems manufactured by the Square D Company include POWERMETER® 600 series and CM 3000™ and CM 4000™ series metering systems. In these systems, a relatively large base unit is provided having extra internal ports available for plugging in options modules which are mounted on cards. The present invention, while useful in such systems, was designed for a power meter requiring a relatively small base unit, wherein the options can be added as separate modules mounted externally to the base unit.